United Kingdom, July 28 -- Marcus Mumford was "amazed" when Kendrick Lamar stripped to "his undies" during a backstage meeting.

The Mumford and Sons star revealed he was once summoned to the rapper's dressing room for a chat after a performance at the Bonnaroo Music Festival in Tennessee and Marcus was left stunned when Kendrick started stripping off as they were talking.

During an appearance on the SmartLess podcast, Marcus explained: "When I was invited, very explicitly invited, backstage was after Kendrick Lamar played Bonnaroo.

"There was a message that came down from on high that Kendrick would like to see you. When Kendrick calls, you come, right, because he's the king."

He added: "He took almost all of his clothes as I walked i...